The principles of an automatic landing system for aircraft disclosed in the Bossler et al U.S. Pat. No. 3,174,146 has been used as an aircraft carrier automatic landing system for some time. The system as used by the U.S. Navy was originally identified as AN/SPN 10, was later updated as AN/SPN 42, is currently in operation as AN/SPN-42A and is now undergoing further updating to be designated as AN/SPN-46. In all forms, however, the basic principles of the aforesaid patent have been used. Specifically, these systems have employed a radar/computer combination in conjunction with space-stabilized approach path for aircraft to determine vertical (altitude) and lateral (azimuth) position errors of an aircraft with respect to this approach path. Command signals are generated by the shipborne computer and are transmitted to the aircraft for automatic operation of its autopilot. Aircraft pitch command signal is generated having a term proportional to the vertical error, a term proportional to the derivative of the vertical error with respect to time, and a term proportional to the time integral of the vertical error. Similarly, aircraft roll command signals are generated having three terms, one proportional to the lateral error, one proportional to the time derivative of the lateral error, and one proportional to the time integral of the lateral error.
The constants of proportionality are varied in programmed fashion as a function of aircraft range and aircraft type as is explained in the aforesaid patent, the disclosure of which is incorporated herein by reference.
Although automatic landing systems of the above type have performed in highly successful fashion over many years of use by the U.S. Navy and others, a practical drawback exists because of the fact that the acquisition/tracking radar system used is of the "augmented" or "cooperative" type. By "augmented" or "cooperative" is meant that each aircraft is provided with some means which aids the radar system in identifying and tracking a known, fixed point on the aircraft. Such means may be, for example, a corner reflector or a beacon transponder. Corner reflectors are not believed to be desirable in view of the fact that, if permanently fixed, they present an excellent target for enemy radar devices. An alternative is to deploy them only during the landing operation. However, the orthogonality requirements for the faces of a corner reflector make the installation and deployment of a foldable corner reflector very difficult. Thus, transponders are currently employed on each aircraft. However, transponders are very complex pieces of equipment and experience has shown that at any given time it can be expected that upwards of 25% of a carrier's available aircraft will suffer transponder malfunction. This means, of course, that in inclement weather or in any condition where visual landing is not feasible or possible, only 75% of the carrier's aircraft may be launched, unless those aircraft having faulty transponders are to be sacrificed through retrieval failure. Although it is conceivable that circumstances could exist which would dictate such sacrifice, it must be considered, at best, as an extreme measure. In consequence of these facts, full strength naval strategy is still influenced by weather conditions and the presence of sufficient visibility to enable visual, pilot controlled landing aboard the carrier.
Naturally, it would be desirable to remove such a constraint and the invention disclosed herein enables same by eliminating any need for "augmentation" or "cooperation" as discussed above.